police sergeant is under investigation over over a video on facebook. in elizabeth wenger is in san francisco with the video that was recorded. >>> this video all over the net. it makes you think why would a san francisco cop ever do this to begin with? we should know he is changing his story now but that video essentially shows the driver starting here at larkin and broadway going through, gunning it through the broadway tunnel, all the way towards chinatown. let's check out that video now. [ sound of engine revving ] >> reporter: so that's the clip of what was posted on the sergeant's page. it appears to show him driving 100 miles per hour in a lamborghini through the broadway tunnel in just seconds. now, there's no way to actually identify who is driving but in the comments section of his facebook page, he even bragged, we were all drunk. folks we talked to say they were mostly shocked. >> there is no points for being smart. >> probably not the smartest thing for someone to do especially in that position. >> no cars in there, i would describe this as simply driving with purpose.